This invention generally relates to communication networks and, more particularly, to powering data transmission lines in a communication network.
Data signals in a communication network commonly are transmitted in a line in accordance with a data transport protocol (i.e., a physical layer protocol of the O.S.I. model). xe2x80x9cT1xe2x80x9d is one such transport protocol in which digital data is transmitted, in the format of a DS1 signal, across copper transmission lines at a rate of about 1.54 megabits per second. Like data signals utilizing other data transport protocols, the signal quality of a signal utilizing the T1 protocol (a xe2x80x9cT1 signalxe2x80x9d) must be restored about every 6,000 feet by repeaters or other signal regeneration devices. In addition, the T1 protocol requires line powering so that equipment such as, for example, a transmitting device may be energized merely by connecting to the transmission line.
T1 signals typically are transmitted from a transmitting device (e.g., a modem) to a destination device (e.g., a central office) via a series of transmission lines and repeaters. Accordingly, a T1 signal requires a relatively large number of repeaters to transmit a single signal many miles. This requirement, however, increases the overall cost of a T1 communications system. The art has responded to this problem by coupling signal converters to the transmission line to convert T1 signals (and their accompanying DS I signals) into fiber optic signals. Once converted, the fiber optic signals may be transmitted long distances, via fiber optic cable, to the destination device. Fewer repeaters thus are necessary. Such signal converters typically include a circuit board having interlace circuitry for receiving a T1 signal (and their accompanying DS1 signals) prior to converting the signal. In addition, signal converters that receive T1 signals include powering circuitry for providing line powering in accord with the T1 protocol. One commonly used signal converter, for example, is a DDM-2000(trademark) signal converter, available from Lucent Technologies Inc. of Murray Hill, N.J.
Although fewer are required when using a signal converter, repeaters frequently are necessary in the portion of the line between the transmitter and the signal converter. Accordingly, there still is a need to reduce the number of repeaters to improve cost effectiveness. The art has responded to this need by developing the High-Bit-Rate Digital Subscriber Line digital data transport protocol (xe2x80x9cHDSLxe2x80x9d). As is known in the art, an HDSL carrier signal typically can be transmitted up to about 2.0 miles over existing copper lines and thus, requires fewer repeaters (if any) between the transmitter and the signal converter. Another advantage of HDSL is that it provides improved signal quality that is comparable to fiber optic data transmission. A DS1 signal may be interleaved upon an HDSL carrier signal to carry such DS1 signal up to about 2.0 miles. For more information relating to HDSL, see xe2x80x9cCopperOptics, Enhancing the Performance and Application of Copper Cable with HDSL: A Technology Brief from PairGain Technologies, Inc.xe2x80x9d at http://www.pairgain.com/copperop.htm.xe2x80x9d
In a manner similar to signal converters that receive and convert T1 signals, signal converters that receive and convert HDSL signals also have a circuit board with both interface circuitry for receiving an HDSL signal prior to conversion, and line powering circuitry for powering the line in accordance with the HDSL protocol. Undesirably, however, the line powering circuitry for the HDSL protocol physically is much larger and generates much more heat than the powering circuitry that may be utilized with the T1 protocol. As a result, a signal converter that can accept four T1 signals may not be large enough to receive four HDSL signals absent significant redesign. For example, the DDM-2000(trademark) signal converter can be configured to receive either multiple independent T1 signals, or one HDSL signal. Accordingly, several times as many DDM-2000(trademark) signal converters are required when using the HDSL protocol than those that are necessary for use with the T1 protocol. Of course, this requirement necessarily increases the ultimate cost of such a data communication network, thus offsetting some of the benefits of utilizing the HDSL protocol.
In accordance with one aspect of the invention, a system for transmitting data signals across a data transmission line in accord with a specified digital data transport protocol utilizes a powering shelf for powering the line. To that end, the line electrically couples the powering shelf with a signal converter that converts the data signals to optical signals. The signal converter includes a first interface for receiving a first data signal complying with the protocol from the line, and a housing. The powering shelf, which is external to the converter housing, preferably includes a first powering circuit for the first interface.
In accordance with another aspect of the invention, the signal converter includes a second interface for receiving, from the line, a second data signal complying with the protocol. The powering shelf correspondingly includes a second powering circuit for the second interface. In preferred embodiments, the protocol is HDSL and the line is a copper line. The powering shelf also may include transmission circuitry that receives and transmits the first data signal without significantly modifying it. In preferred embodiments, the transmission circuitry includes a one to one transformer.
The first data signal may be transmitted from a transmitting device and the powering circuitry may be configured to power the transmitting device. In some embodiments, the transmitting device is an HDSL modem. Moreover, the powering shelf may include signal converter powering circuitry for powering the signal converter, or it may include sealing current circuitry for providing sealing current to the line. The powering shelf also may include circuitry for providing a current of no greater than about 100 milliamps, and a voltage of up to about 200 volts.
In yet other aspects of the invention, the powering shelf may include powering circuitry for powering the line in accord with the protocol, an input line interface for receiving data signals from the line, and an output interface for transmitting data signals to the line. In preferred embodiments, the powering shelf is external to the signal converter housing and communicates with the signal converter via the line.